People get to define their own sexual boundaries. There's nothing wrong with me saying I want a MMF threesome but won't to a FFM threesome. Those are my boundaries. My partner doesn't get to agree to something, and then after the fact claim I "owe" them an experience that crosses my boundaries. That's favor-sharking. If someone only wants to do some type of sexual thing in exchange for some other type of sexual thing, they need to inquire about that before they do their thing, not do it and say "Now it's my turn to do it my way."

You're not guaranteed a certain type of sexual experience that violates your partners boundaries just because you agreed to do something else sexual with them. IT'S OKAY FOR ANYONE TO WANT ONE TYPE OF THREESOME BUT NOT ANOTHER. And if you're agreeing to do sexual things you don't actually want to do because you're a "pleasing type," it sounds like you would really benefit from therapy.

IT'S NOT SELFISH TO HAVE SEXUAL BOUNDARIES.